1. Field of the Invention
The present invention relates to a radio LAN (local area network) master station system, in particular, relates to such a system which has a specific antenna system.
2. Description of the Related Art
Lately, a radio LAN system in 2.4 GHz band has been utilized widely.
However, that frequency band, 2.4 GHz band, is also used for ISM (Industrial Science Medical) band. Therefore, a radio system which uses such frequency band is apt to be interfered by an ISM band system, such as a microwave oven. Nevertheless, a radio LAN system using 2.4 GHz band is popularized rapidly, since no license nor qualification is requested for the operation of that system, and no communication fee is charged by a communication company when the system is installed.
A radio LAN system is used not only indoors, but also out of a room in a communication manner such as a point—point manner, and/or a point-multipoints manner.
FIG. 1 shows a prior art radio LAN system in a point-multipoints manner, in which a single master station having a single wide angle antenna and a single transceiver, and a plurality of client terminals. A wide angle antenna is used in a radio LAN master station which operates in a point-multipoints manner out of a room, so that wide area can be covered by a single master station.
However, the radio LAN master station in FIG. 1 has a disadvantage that it suffers from interference by a similar LAN system closely located, and/or by another system using the same frequency band. Further, communication quality is much degraded because of multi-path propagation. In FIG. 1, radio wave emitted by a client terminal 1-3-1 is received by a master station 1-1-1 through an antenna 1-1-2 not only as direct wave 1-2-1, but also as reflection wave 1-2-2 which reaches the antenna 1-1-2 through reflection by a building 1-2-3 which locates close to a direct path between a master station and a client terminal. A reflected wave is an undesired interference wave in a master station.
The radio LAN master station system in FIG. 1 having a single wide angle antenna has further disadvantage that no long communication is possible because a wide angle antenna has small gain.